Problem: $ \left(\dfrac{16}{81}\right)^{-\frac{1}{2}}$
Solution: $= \left(\dfrac{81}{16}\right)^{\frac{1}{2}}$ To simplify $\left(\dfrac{81}{16}\right)^{\frac{1}{2}}$ , figure out what goes in the blank: $\left(? \right)^{2}=\dfrac{81}{16}$ To simplify $\left(\dfrac{81}{16}\right)^{\frac{1}{2}}$ , figure out what goes in the blank: $\left({\dfrac{9}{4}}\right)^{2}=\dfrac{81}{16}$ so $ \left(\dfrac{81}{16}\right)^{\frac{1}{2}}=\dfrac{9}{4}$